The present application is related to U.S. Ser. No. 60/019,590, the contents of which are hereby incorporated by reference.
Chiral bisphosphines are an important class of chiral ligands that are used to prepare catalysts for the asymmetric homogeneous hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration or hydroformylation of olefines, ketones, imines as well as the enantioselective isomerisation of olefins, the coupling of Grignard reagents and organic halides and the arylation of olefins, e.g., the Heck reaction. A good summary of these reactions is contained in R. Noyori, Asymmetric Catalysis in Organic Synthesis, John Wiley & Sons, 1994 and I. Ojima, Catalytic Asymmetric Catalysis, VCH Publishers, 1994. Known chiral bisphosphines are the following classes: bisphosphines derived from natural products such as DIOP or NORPHOS; bisphosphines with chiral P, such as DIPAMP; substituted 1,2-bis(phospholano)benzene ligands (DuPHOS); and axial chiral compounds of appropriately substituted sterically hindered biphenyls. The most prominent and the synthetically most useful members of the latter class in particular and of known chiral bisphosphines in general are BINAP and TolBINAP, of the structure ##STR2##
Asymmetric catalysts based on BINAP often provide high enantiomeric excess (ee) in a variety of reaction types. Unfortunately, a number of substrates or reactions result in undesirably low ee, so that more cumbersome classical resolution procedures have to be applied.
In the present invention a novel set of bisphosphine ligands is described, which are appropriately substituted cyclophanes with planar chirality. The present invention covers enantiomers of pseudo-ortho substituted cyclophanes. In one example, the bisphosphines of the present invention form complexes used to synthesize a chiral intermediate for the AIDS drug CRIXIVAN.RTM. (trademark of Merck & Co., Inc.).
The chiral biphosphines of the present invention provide desirably high enantiomeric excess as catalysts in a variety of asymmetric reactions.